Sex differences in sensorimotor function in young adults

Purpose. To determine whether sex differences in sensorimotor function in young adults are generalised or parameter-specific, and to establish which components of sensorimotor regulation differ, using a large computerised assessment dataset analysed separately for each hand. Materials & Methods. Seven hundred and forty-five apparently healthy young adults (493 men, 252 women; mean age 21.4±2.6 years) were examined with the computerised movement meter (CMM). Twelve sensorimotor parameters were analysed for each hand (24 in total): movement-cycle duration; flexion- and extension-realisation times; switching of the central set; short-term motor memory; simple reaction time to light and to sound; flexor and extensor correction error; movement smoothness; and the extensor–flexor balance with and without visual control. Because motor control is contralateral, the right hand was taken to index the left hemisphere and the left hand the right hemisphere; no derived asymmetry index was computed and handedness was not modelled. Sex differences were tested with two-sided Mann–Whitney U tests, effect sizes were expressed as rank-biserial correlations (rbc) with 2,000-sample bootstrap 95% confidence intervals, and family-wise error across all 24 parameters was controlled by the Benjamini–Hochberg false-discovery-rate procedure (q<0.05). Results. Six of the 24 parameters differed reliably after control of the false discovery rate, and all effects were small in magnitude (|rbc| 0.11–0.27). Simple reaction time to light was longer in women for both hands (right hand rbc=+0.19, q=0.001; left hand rbc=+0.27, q<0.001), the two largest effects in the dataset, whereas simple reaction time to sound did not differ for either hand. Three left-hand (right-hemisphere) parameters differed as well: the extensor–flexor balance was displaced towards the extensor phase in women, both with visual control (rbc=+0.16, q=0.003) and without it (rbc=+0.12, q=0.033), the latter reflecting a flexor displacement in men, and short-term motor memory was longer in women (rbc=+0.11, q=0.045); none of their right-hand homologues approached significance. Switching of the central set for the right hand (left hemisphere) was longer in men (rbc=−0.13, q=0.028), that is, women reorganised the central set faster on that side. No reliable differences were found for movement-cycle duration, flexion- and extension-realisation times, flexor and extensor correction error or movement smoothness. Conclusions. Sex differences in sensorimotor function in young adults are parameter-specific and small rather than global. The slower visual reaction in women occurred without any accompanying loss of accuracy or smoothness, and the hand-specific differences clustered in right-hemisphere-dependent spatial-retentive parameters, the single left-hemisphere difference concerning an executive rather than an executional index. Sex-stratified reference values are therefore warranted for these six parameters, and in particular for switching of the central set, which is used as a marker of central regulation in the monitoring of athletes, whereas the remaining parameters may reasonably be pooled across sexes. The phase of the menstrual cycle was not controlled, which precludes inference about the hormonal mechanism.